Parabolic reflector



Feb. 29, 1944. Y BOERNER 2,342,721

PARABOLIC REFLECTOR Filed 0G12. 10, 1941 /n venl'or: I

Patented Feb. ze, 1944 UNITED PARABOLIC REFLECTOR Rudolf Boerner,Berlin, Germany; vested in the Alien Property Custodian ApplicationQctober 10, 1941, Serial No. 414,479 In Germany January 20, 1940 (Cl.Z50-11) 3 Claims.

This invention relates to the directional transmission of intelligenceand is more particularly concerned with arrangements of .the kind havinga parabolic reector and a radiator in the focus thereof.l

According to the invention a convex mirror, that may be of parabolic orhyperbolic shape or may be of the globular, cylindrical or any similartype, is disposed in front of the radiator arranged in the focus, aswill be understood from the following description and the acccnipanying`drawing,l in which Fig. 1 is a diagrammatic sectional View of a priorarrangement, Fig. lo is a diagrammatic sectional View showing oneembodiment of the invention, Fig. 2 is a graph which illustratesradiation conditions, Fig. 3 is a diagrammatic sectional view of anarrangement similar to that shown in Fig. 1b, Fig. 4a is a diagrammaticsectional View illustrating an improvement upon the arrangement shown inFig. 1b, Fig. 4b` is a diagram of the radiation pattern produced by thearrangement according to Fig. 4a.

In many cases, as when transmitting secret communications, theradiation-collecting effect should as far as possible be small, that isto say, should be quasi optical, in order on the one hand to reduce thelistening range and on the other hand to enable the use of small sendingpower. The customary reflectors, being somewhat large in depth have agreat collecting effect. Also, the use of such large reflectors meetswith difficulties which for economical reasons make it desirable torestrict the collecting effect.

In prior arrangements the direct radiation in the case of parabolicreiiectors is either collected with the aid of a separate wave channelor is directed against the reflector in order to underso totalreflection.

For instance, as shown in Fig. 1a,a sof-called calotte A, formed as aconcave mirror of semiglobular or other suitable shape, is arranged toutilize the direct radiation in a manner to light up the reflector B andthereby to prevent the direct rays and the reflected rays frominterfering outside the reflector. A calotte so arranged does notimprove the directivity rand is suitable only in the case of reflectorshaving a large focal distance and a small depth. In the case of all theother reflectors the efliciency is impaired in the mid-zone by aso-called shading eifect due to the screening property of the calotte A.

The novel system shown in Fig. 1b has a refleeting calotte formed as asort of convex opti cal mirror C by which the direct rays from aradiator S, located in the focus of reflector B, are guided in a specialmanner. In fact, the rays .are reflected by mirror C and then byreflector B so that the rays outgoing from the reflector are notparallel to its axis but converge or run toward it. As a result, thedirectivity of the radiation characteristic is increased by values up toWhile the detrimental shading effect of concave mirrors, such as mirrorA, Fig. la, is obviated.

Another advantage due to mirror C is that the l secondary maxima arisingin the case of higher maxima of reflection are reduced, as can be seenin Fig. 2.

Instead of one radiator S a number of radiators or groups thereof may beprovided. For instance, Fig. 3 shows two radiators Sl, S2.. F denotesthe focus of reflector B.

As shown in Fig. 4a an additional radiator S may be arranged withinmirror C in order to produce an additional directive beam. This is notpossible in prior devices.

The latter arrangement is particularly suitable for producing radiationpatterns to be followed by ships, the broad directional beam serving togive a presignal.

What is claimed is:

1. A directional wave transmitter comprising a concave parabolicreflector, a source of radio frequency energy located at the reiiectorfocus, the arrangement being such that Waves radiating from the sourcewill be reflected in parallel beams, a shield located on the reflectoraxis beyond the focus in position to intercept outwardly directed wavesfrom said source, and means for projecting a substantial portion of saidintercepted energy into the axial zone beyond saidv in claim 1, in whichthe reflector extends axially beyond the mirror surface.

3'. An arrangement according to claim 1, wherein the said convex mirrorsurface is a parabolic reector.

RUDOLF ,BOERNER

